But of course, with only 47% of air mass flow through the radiator, you also have only 47% of air mass flow through the engine and 47% as much heat to reject.  So, for an NA engine, there shouldn't be a significant change in the ability of a cooling system.
Or so it seems to me .... Jim S.

Ed Anderson wrote:

Found a table of air density vs Altitude

Sea level Density = .00237 Slug/Ft^3
Density at 20,000 = 0.001267 Slug/Ft^3 or a 47% decrease

So taking formula for air mass  W = p*V*A with p 47% less than at sea level
means you would get 47% less air mass flow (with the same cubic feet/minute
of air volume flow) at 20,000 ft compared to what you would get at sea level
for the same volume flow.

While cooler temps would help, it would not compensate for a 45% less air
mass flow.

Ed

Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com

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Jim Sower
Crossville, TN; Chapter 5
Long-EZ N83RT, Velocity N4095T